The present invention relates to air conditioning systems, and more particularly to modifications of such systems to reduce power consumption and recover waste heat.
Most home and small commercial air conditioning systems employ a closed vapor compression/expansion cycle with heat rejection to ambient air. Such systems include an evaporator portion with a refrigerant expansion valve, an evaporator, and a house air circulation fan, and a condenser portion with a compressor, an air condenser, and an air condenser fan. Warm air is passed over the evaporator coil, where it is cooled by the transfer of heat to the liquid refrigerant flowing therethrough. The cooled air then passes to the interior of the building or other enclosure desired to be cooled. The refrigerant is converted to a vapor by absorbing the heat from the warm air. The vaporized refrigerant then flows to a compressor where it is compressed to a high pressure vapor, in the process being heated to a temperature higher than the temperature of the available heat sink medium. The vapor then flows to the condenser, where it is condensed to a liquid by transfer of its sensible and latent heat to the heat sink medium, which is typically ambient air. The high pressure liquid then flows through a throttling device such as an expansion valve or capillary tube, where the pressure and temperature of the liquid are reduced to the conditions existing in the evaporator. In particular, the temperature of the liquid refrigerant is reduced to a point below the temperature of the air being cooled, thus completing the refrigerant cycle.
According to the basic thermodynamics of the vapor compression refrigeration cycle just described, the amount of energy required to operate the compressor is a function of the pressure and temperature of the refrigerant in the evaporator and the condenser. The condenser pressure and temperature are in turn dependent upon the temperature of the heat sink medium, typically ambient air. In general, the power consumed by the compressor is thus directly proportional to the temperature of the heat sink medium. Consequently, it is advantageous to utilize a low temperature heat sink medium where possible to reduce the power consumption of the compressor. In larger commercial applications this is often accomplished by the use of cooling towers, wherein water is used to absorb the waste heat from the air conditioner and is subsequently evaporated to ambient air. The evaporation process effectively reduces the heat sink temperature of the air conditioner.
It may also be desirable to further conserve energy by recovering the heat rejected to the heat sink medium rather than rejecting the heat to the ambient air. It is well known in the art that the power consumption of an air conditioning system can be decreased by the use of a low temperature heat sink medium, while at the same time recovering the rejected heat for useful purposes. Systems utilizing swimming pool water as a heat sink medium, wherein the need for a swimming pool heater is reduced or eliminated by the simultaneous heating of the water, are disclosed in Poteet U.S. Pat. No. 4,019,338; Davies U.S. Pat. No. 3,976,123; and Webber U.S. Pat. No. 3,926,008. Systems for rejecting the waste heat of a refrigeration system or heat pump to a domestic water supply, thereby heating the water, are disclosed in Schmidt U.S. Pat. No. 3,916,638, and Wetherington, Jr. et al. U.S. Pat. No. 3,922,876.
The above-mentioned systems differ from the present invention in several important aspects, particularly with respect to energy conservation. The patents to Wetherington, Jr. et al, Schmidt and Davies, and one embodiment of the patent to Webber, describe a system wherein the liquid cooled heat exchanger is placed in series with the compressor and the condenser of a conventional refrigeration loop. The disadvantage of such a series arrangement is that it results in a higher refrigerant pressure loss through the system than exists in a conventional refrigeration loop, because the refrigerant must pass through both condensers during every cycle. Instead of conserving energy in the air conditioning loop, these systems actually require more energy for compressor operation than does a conventional system.
in the patent to Poteet, and in another embodiment of the patent to Webber, systems are disclosed wherein the liquid cooled heat exchanger is plumbed in parallel with the air condenser of the conventional refrigeration loop. However, these systems make no provision for refrigerant level control to exhaust the liquid refrigerant from the unused condenser. The refrigerant level may therefore vary significantly throughout The loop, and in particular the refrigerant may tend to collect in the unused condenser because of the temperature differential between the condensers. Thus these systems may require additional energy for adequate compressor operation instead of achieving energy conservation. Further, these systems as disclosed provide for the condenser to be submerged in the swimming pool, a configuration that greatly increases the refrigerant pressure drop due to the length of the plumbing required and leads to a potential loss of liquid subcooling.
The patents to Davies, Webber and Poteet also contain disadvantages with respect to energy conservation in their utilization of the waste heat of the air conditioning system. These patents describe systems wherein the swimming pool water flows continuously through the water side of the liquid cooled condenser, which is placed in series with the existing pool pump and filter system. The resulting pressure loss through the pool filter loop when the air conditioner is inoperative requires increased energy input to the pool pump, thus failing to conserve energy in the overall system.
A further disadvantage of the patent to Wetherington, Jr. et al and like patents related to the art of heating water for a domestic water supply with the waste heat of an air conditioning system, is that these patents utilize only the "superheat" portion of the waste heat for heating, exhausting the remaining heat through a conventional air condenser. The amount of energy available in the superheat region is quite small compared to the total energy available in the superheat, condensing and subcooling regions, and therefore these systems do not achieve maximum energy conservation and utilization. The system disclosed in the patent to Schmidt avoids this problem by using two water-cooled condensers, but is therefore limited in its ability to be retrofitted into an existing air conditioning system having an air condenser.